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Abstract

We investigate the interband transitions in several ensembles of
self-assembled InAs/GaAs quantum dots by using photoluminescence
excitation spectroscopy under strong magnetic fields up to 28 T.
Well-defined resonances are observed in the spectra. The magnetic field
dependence of the resonance energies allows an unambiguous assignment
of the interband transitions which involve both discrete states of the
quantum dots and wetting layer states. A strong anticrossing between
two transitions is observed in all samples, which cannot be accounted
for by a purely excitonic model. The coupling between the mixed
exciton-longitudinal optical (LO) phonon states is calculated using the
Frohlich Hamiltonian. The excitonic polaron energies as well as the
oscillator strengths of the interband transitions are determined. An
anticrossing is predicted when two exciton-LO phonon states have close
enough energies with phonon occupations which differ by one. A good
agreement is found between the calculations and the experimental data
evidencing the existence of excitonic polarons.